Directory listing fails on larger folders

I am experiencing a very strange behavior: I have two computers behind a netgear router, which act differently when connecting to a particular site. The first computer is running Win 2000 and can access my FTP site with absolutely no problems. The second computer is running Win XP and can access my FTP site, but when I click on certain folders it times out while trying to retrieve a directory listing. The problem folders happen to contain more files than the ones that work OK (as few as 29 and possibly fewer). On this same computer I can view the content of the larger folders in the command line FTP that comes with XP, but I get the same problem in IE as I do with SmartFTP. I have tried both active and passive FTP. The server is running IIS 5 FTP.